1. Technical Field of the Invention
The present invention relates to photostabilizing at least one dibenzoylmethane derivative against UV radiation employing at least one merocyanine sulfone derivative.
This invention also relates to novel compositions, in particular cosmetic compositions for topical application.
2. Description of Background and/or Related and/or Prior Art
Light radiation with wavelengths in the range 280 nm to 400 nm is known to brown the human epidermis; more particularly, rays with a wavelength in the range 280 to 320 nm, known as UV-B, are known to cause erythema and cutaneous burns which may be deleterious to the development of a natural tan. For those and for aesthetic reasons, there is a constant demand for means for controlling natural tanning which can thereby control the color of the skin; thus, UV-B radiation must therefore be screened.
It is also known that UV-A rays with wavelengths in the range 320 to 400 nm, which cause the skin to brown, tend to induce an impairment therein, in particular with sensitive skin or skin which is continually exposed to solar radiation. In particular, UV-A radiation causes the skin to lose elasticity and the appearance of wrinkles, resulting in premature aging of the skin. The radiation encourages triggering the erythematous reaction or amplifies that reaction in certain subjects and may even be the cause of phototoxic or photo-allergic reactions. Hence, for aesthetic and cosmetic reasons, such as preserving the natural elasticity of the skin, for example, more and more individuals seek to control the effect of UV-A radiation on their skin. Thus, screening UV-A radiation is also desirable.
With the goal of ensuring protection of the skin and keratinous substrates against UV radiation, sunscreen compositions are generally used which comprise organic screens which are active in the UV-A and active in the UV-B regions. The majority of such screens are liposoluble.
In this respect, a current particularly advantageous family of UV-A screens is constituted by dibenzoylmethane derivatives, in particular 4-tert-butyl-4′-methoxydibenzoyl methane, which have intrinsically good absorbing powers. Such dibenzoylmethane derivatives, which are now well known per se as screens which are active in the UV-A region, have been described in FR-A-2,326,405 and FR-A-2,440,933, as well as in EP-A-0,114,607; 4-tert-butyl-4′-methoxydibenzoyl methane is currently marketed under the trademark “Parsol 1789” by ROCHE VITAMINS.
Unfortunately, it has been discovered that dibenzoylmethane derivatives are relatively sensitive to ultraviolet radiation (in particular UV-A), i.e., more precisely, they have an annoying tendency to degrade at a greater or lesser rate under the action thereof. This substantial lack of photochemical stability of dibenzoylmethane derivatives to the ultraviolet radiation to which they are by their very nature intended to be subjected cannot guarantee constant protection during prolonged exposure to the sun, and repeated applications at regular, close intervals have to be made by the consumer to effectively protect the skin against UV radiation.